1. Field of the Invention
The invention relates to speed changing apparatus, and in particular to a unit which is adapted to mount an engine on an aircraft for changing the speed of the aircraft propeller. More particularly, the invention relates to such a unit having an adjustable eccentrically mounted stationary shaft which can be manually rotated to a selected fixed position to change the drive ratio between the propeller and a belt connected drive shaft pulley.
2. Description of the Prior Art
Most model aircraft are driven by gas engine driven propellers in which the propeller is mounted directly on the engine drive shaft to supply the power and thrust for the aircraft. Various aircraft operating and flight characteristics can be achieved by changing the propeller size or the speed at which the propeller is driven. This enables various operating characteristics and performance levels to be achieved by the model aircraft, many of which are remote or radio controlled.
Heretofore, the propeller size and configuration had to be changed in order to achieve these various operating characteristics since the speed of the drive shaft remains constant dependent upon the particular engine being used for turning the propeller. Otherwise, a different engine with different torque and speed characteristics would be required to replace the existing engine. Such changeovers are expensive and time consuming to most model aircraft owners and operators.
Recently, motorized or engine powered hang gliders have been developed, also referred to as powered foot launched aircraft. These aircraft also use an engine driven propeller to provide the thrust for driving the aircraft. It also is desirable to be able to adjust the amount of thrust and the operating characteristics, such as the speed and thrust of the propeller for these foot launched aircraft. This enables different flight characteristics to be achieved which can be adjusted in relationship to the weight and strength of a particular pilot, wind and weather conditions at time of flight, and particular terrain over which the aircraft is to be flown.
It also is difficult for many aircraft designs to change the existing engine with a different type or size engine without considerable modifications to the frame due to the particular engine mounting arrangement used for each type of aircraft.
Therefore, the need has existed for a speed changing unit in which the engine is mounted directly on the unit, which in turn is mounted on the frame of an aircraft to eliminate modifying the aircraft and components thereof for mounting of the engine directly to the aircraft frame, as in prior constructions. Furthermore, the speed changing unit should enable the propeller speed to be adjusted to meet desired flight characteristics for the aircraft without replacing the engine or propeller itself in a simple, economic and convenient manner.
Prior aircraft speed changers have used a pair of spaced rotating shafts, each of which has a pulley mounted thereon with a connecting drive belt extending therebetween. One of the shafts is the engine drive shaft. The propeller is mounted on the other or driven shaft. This driven shaft must be rotatably supported in bearings with the belt engaged pulley and propeller being fixed on the shaft for rotation with the shaft. In order to change the thrust or speed of the aircraft and propeller, various size pulleys are used with complementary size belts. This requires replacement both of the pulley and drive belt each time a different speed and thrust characteristic is desired. This requires additional components with the increased cost factors.
In nonanalagous art, an eccentric mechanism has been used to avoid replacing the drive belt for each different size drive pulley. One such arrangement is shown in U.S. Pat. No. 1,323,490 for a grinding machine. Such an eccentrically mounted drive arrangement uses a pair of spaced shafts, both of which are rotatably mounted, and in which the eccentrically mounted pulley shaft is the drive shaft. This arrangement requires three separate components, namely, a shaft, a pulley fixedly mounted on the shaft, and a propeller fixedly mounted on the extended end of the shaft. All of these components require increasing unnecessarily the weight of the unit which is undesirable for aircraft application.
Thus, there is no speed changing unit of which I am aware that is intended primarily for changing the speed and thrust of an aircraft propeller, which uses an eccentric mounting arrangement having a stationary shaft with a pulley-propeller assembly rotatably mounted thereon which requires only replacement of a single pulley on the drive shaft and manual adjustment of the eccentric for achieving various operating and flight characteristics for the aircraft.